The results of high-field stressing experiments for dry oxides, pyrogenic oxides, nitrided pyrogenic oxides and reoxidized nitrided pyrogenic oxides are presented in this paper. Pyrogenic oxides show poor high-field properties, but nitridation and reoxidation improves them considerably. In fact, the high-field performance of reoxidized nitrided pyrogenic oxides is even superior to that of dry oxides. Our results indicate that improvement occurs due to inhibition of hydrogen drift.